2721 WETMORE AVE MARQUEE APARTMENTS Geotech Report 2023-06-22

Subsurface Exploration, Geologic Hazard,and 2721 Wetmore Preliminary Geotechnical Engineering Report Everett, Washington Project and Site Conditions brownish orange, fine to coarse sand with some amounts of silt ranging to silty, trace amounts of gravel, and trace amounts of organics. The observed thickness of the fill ranged generally less than 5 feet at the locations of our borings. However, fill may be present at greater depths in other areas of the site not explored. Vashon Lodgement Till The lodgement till sediments were encountered directly underlying the fill and extended to depths of 23 to 33 feet below the ground surface. The lodgement till generally consisted of medium dense to very dense, moist, olive, non-stratified silty to very silty fine to coarse sand with trace to some amounts of gravel. Lodgement till sediments typically exhibit a characteristic diamict fabric and generally consist of a poorly-sorted mixture of sediment that was deposited at the base of the Vashon glacial ice. The basal portion of the lodgement till can sometimes have the appearance of advance outwash where it was deposited in close proximity to the fluvial system in front of the advancing ice sheet. Lodgement till sediments were overrun by several thousand feet of ice during the last glacial advance resulting in a very dense soil possessing high-strength, low-compressibility, and low-permeability characteristics. The upper several feet of the lodgement till can be iron-oxide stained and in a loose to medium dense condition as a result of past weathering processes. The lodgement till is suitable for support of building foundations; however, the siltier portions of the unit can deteriorate rapidly if disturbed while in a wet condition. These sediments can be used in structural fills, and the ability to achieve suitable compaction and performance of the fill will depend mostly on the moisture content at the time of placement. At the time of our subsurface investigation program, the observed moisture content of the lodgement till was at or above that necessary to achieve the required level of compaction needed for use as structural fill. Some moisture- conditioning (wetting or drying) may be required depending on the time of year construction occurs. Vashon Advance Outwash Sediments interpreted as Vashon advance outwash were encountered below the units described above to maximum depths drilled of 41.5 feet in borings EB-1 and EB-2 on the west side of the site. Advance outwash sediments generally consist of dense to very dense, moist, olive to grayish olive, stratified, fine to medium sand with trace to some amounts of silt and fine to coarse sand with trace amounts of silt. Portions of the advance outwash were observed to be very silty and can be gravelly. Rare thin (<_ 3 inch thick) silt interbeds were also observed. The Vashon advance outwash consists of sediments that were deposited by meltwater streams that emanated from the advancing glacial ice during the Vashon Stade of the Fraser Glaciation, approximately 15,000 years ago. Advance outwash sediments were subsequently overridden and compacted by the weight of the overlying ice. May 28,2019 ASSOCIATED EARTH SCIENCES, INC. FSM/Id-190168E001-2-Projects\20190168\KE‘WP Page 4